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ADR 0001: Keep Harrier As A Headless MCP Server

Status

Accepted.

Context

Harrier is designed to help AWS DevOps Agent investigate EMR, Spark, and Kubernetes failures. The operator already works in an MCP-capable agent experience, and the highest-value work for Harrier is evidence collection, classification, report generation, and safe recommendation preparation.

Adding a standalone chat UI would increase maintenance scope, duplicate the client experience, and distract from runtime coverage and diagnosis quality.

Decision

Harrier EMR MCP remains a headless MCP server. It exposes structured tools and human-readable report output, but does not own an interactive chat UI.

The demo lab remains a separate repository because it creates disposable AWS resources and live Spark scenarios. The MCP repository remains focused on production server behavior, contracts, safety, and deployment.

Consequences

  • AWS DevOps Agent and other MCP clients own the conversation UI.
  • Harrier can prioritize stable tool contracts, bounded evidence, and readable reports.
  • Examples and prompt docs become important because they show clients how to present Harrier output well.
  • Any future UI should be evaluated as a separate package or repository, not folded into the core server by default.